The present invention relates to a brake slip control apparatus fed with auxiliary energy for use in a vehicular hydraulic brake system. The apparatus comprises a master cylinder assembly actuatable by the brake pedal and incorporating a master cylinder piston and an assigned prechamber, with a supply bore and with the delivery of auxiliary energy into the working chamber of the master cylinder. A resetting piston which is axially slidable between stops is arranged on the secondary side of the master cylinder piston, the resetting piston having a larger external diameter than the master cylinder piston and being centrically guided through the shank or an actuating rod of the master cylinder piston in a sealed relationship thereto. The master cylinder piston being caused to assume a defined position on acutation of the brake pedal and in the event of the secondary side of the master cylinder piston being applied by auxiliary energy during slip control.
In a known vehicular brake system of this type (P 30 40 562.0), on the secondary side of the master cylinder piston there is provision of a positioning piston which is axially slidable against an axial stop formed fast with the housing and which is sealed relative to the master cylinder housing. The positioning piston having a larger external diameter than the master cylinder piston and the master cylinder piston rod being centrically guided therethrough in a sealed relationship therewith. On depression of the brake pedal and on application of the secondary side of the master cylinder piston with auxiliary energy during slip control, the pedal-side enlarged circumferential end of the master cylinder piston rod or a circumferential projection of a throttle valve of a throttle valve assembly, which is possible inserted upstream, is movable into engagement with an assigned pedal-side circumferential edge of the positioning piston such as to cause the master cylinder piston to assume a defined position during braking with slip control.
However, this known vehicular brake system bears the disadvantage that during control action there is the inherent risk that, when braking is effected at low frictional values, the brake pedal will be displaced in the direction of the master cylinder as far as until the booster piston is abutting on the positioning tube. It is an object of the present invention to improve upon the known positioning device such as to ensure on control action even under extreme conditions that the brake pedal assumes a position which was precisely defined beforehead. In addition, the positioning tube is to be designed such that no kick of resetting will be felt at the brake pedal.